Orthogonal polarization multiplexing transmission apparatus and multiplexing method used for the same

An orthogonal polarization multiplexing transmission apparatus capable of performing dispersion compensation considering a short wavelength side and a long wavelength side of a zero dispersion wavelength. A plurality of light signals of different wavelengths are divided into two orthogonal polarization multiplexing portions, and the light signals of an oddnumber array polarization multiplexing portion and an even-number array polarization multiplexing portion are orthogonal-polarization-multiplexed in each orthogonal polarization multiplexing portions. Adjacent light signals of the two orthogonal polarization multiplexing portions have their mutual planes of polarization rendered non-orthogonal when multiplexed by an optical multiplexer so that, for the purpose of deterring inter-symbol interference, a guard hand having the wavelength spacing rendered wider than that on orthogonal polarization multiplexing is provided in advance.